syscall: correct spelling/typos in comment

Change-Id: Ib44c6b1ce07aa8fb67033cf21e177a90fd4005dc
Reviewed-on: https://go-review.googlesource.com/21002Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/syscall/mkall.sh

@@ -156,8 +156,8 @@ freebsd_arm)
 	mkerrors="$mkerrors"
 	mksyscall="./mksyscall.pl -l32 -arm"
 	mksysnum="curl -s 'http://svn.freebsd.org/base/stable/10/sys/kern/syscalls.master' | ./mksysnum_freebsd.pl"
-	# Let the type of C char be singed for making the bare syscall
-	# API consistent across over platforms.
+	# Let the type of C char be signed to make the bare syscall
+	# API consistent between platforms.
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs -- -fsigned-char"
 	;;
 linux_386)
@@ -189,8 +189,8 @@ linux_arm64)
 		exit 1
 	fi
 	mksysnum="./mksysnum_linux.pl $unistd_h"
-	# Let the type of C char be singed for making the bare syscall
-	# API consistent across over platforms.
+	# Let the type of C char be signed to make the bare syscall
+	# API consistent between platforms.
 	mktypes="GOARCH=$GOARCH go tool cgo -godefs -- -fsigned-char"
 	;;
 linux_ppc64)